Controller for induction motors



Feb. 19.43. E. w SEEGER ET AL 2,309,794

CONTROLLER FOR INDUCTION MOTORS Filed Feb. 23, 1942 L {7S mrwifvbr ENMMME Patenterf; Feb. 5943 UNITED STATES PATENT OFFICE CONTROLLER FORINDUCTION MOTORS poration of Delaware Application February 23, 1942,Serial No. 432,062

6 Claims.

' ited thereto, is particularly applicable to the control of alternatingcurrent motors driving printing presses and the like.

Printing presses are usually controlled from pushbutton stations, whichstations are equipped with individual pushbuttons which are actuated forstarting, stopping, inching, and the like. When the starting or runningbutton is depressed, it is usually desired to start the press and bringit up to a desired preset speed. When the inching button is depressed itis desired to operate the press, but only as long as the inching buttonis depressed, at a certain minimum speed which is usually lower than thelowest running speed. It is also desired that after depression of thestopping button; or upon failure ofpower'; or upon the occurrence of anydisarrangement of the press, that when subsequently restarting the motorwill have a definite optimum part of its total secondary resistanceinserted in circuit.

An objectof the present invention is to provide a controller of theaforementioned type which provides for gradual stepless accelerationfrom one speed to another during the starting of the press.

Another object is to provide a controller in which the same resistanceand operating means are employed for threading, inching and running.

Another object is to provide a controller comprising a main motorcontroller, and a presetting control station, requiring a minimum numberof connecting wires between the control station and the main controller.

Another object is to provide a controller which insures automatic returnof the control elements to the minimum speed position upon operation ofthe stop pushbutton, and insures such positioning of the controlelements prior to restarting of the motor after voltage failure.

Another object is to provide a controller which after stopping of themotor is always ready for restarting without excessive current.

Another objeofis to provide a controller of the I The system comprises aprinting press (not shown), which is to be operated by an alternatingcurrent motor I, supplied with electrical energy from the bus bars U, L,L of a threephase alternating current system. The motor is of theslip-ring type and has a primary or stator winding provided withterminals I, i and I and a secondary or rotor winding connected to sliprings I I and I. The stator winding may be connected to the lines L Uand L by means of an electromagnetic switch 2, which is provided withnormally open main contacts 2, 2 and 2, for connecting the primarywinding of the motor to the power supply lines L L and L respectively.The switch 2 also has an energizing winding 2' and normally openauxiliary contacts 2.

A variable resistor 3, comprising three sections 3", '3 and 3, one foreach phase, is connected to the secondary winding of the motor. Thevalues of the resistors 3, 3 and 3 may be varied by means of acommutating brush 4 which is connected to, but insulated from, atraveling nut i to move therewith. The traveling nut 5 engages athreaded stem 6, which is driven by a reversible single phase motor 1,having an energizing winding including line terminal 1 and reversingterminals I and P. It the motor I is rotated in one direction or theother by the selective connection ,of the terminal 'l or 1, the stem 6rotates. thereby reciprocating the nut 5 and with it the commutator 4which latter varies the resistors 3', l and 3 of the motor I, to varythe speed of the latter.

Arranged in proximity to the commutator 4, is a potentiometer receiverrheostat or resistor 8, which is connected across the lines L and L, andwhich is provided with a commutator brush 9, the latter beinginsulatedly attached to the traveling nut 5 to move therewith. The brush9 completes a circuit between the resistor 8 and a contact bar it.Connected between the lines L and L is a potentiometer sender rheostatII, which has a variable high speed section li provided with a movablecontact H, a low speed section i l, provided with a number of selectabletaps li and a creeping speed tap li The contact II is connected throughnormally open contacts lI of a relay'll, contact 18 and contactor i8 ofa safety switch IS, the coils I! of a center-biased reversing relay l2,to the contact bar It, and from there through the brush 9 to thereceiver rheostat 8.

The relay I2 is provided with a center pivoted arm l2, to the ends ofwhich are attached magnetic cores lZ for the coils H. The coils I! arestationary, and the magnetic cores are capable of moving axiallyrelatively to the former. The relay arm ii is provided with a movablecontact arm i2", which is arranged to make contact with stationarycontacts I! and I2, respectively, upon deflection of the arm 12 from thecenter position in one direction or the other. The contact arm I2 isconnected to the line L while the contacts I2 and II are respectivelyconnected through limit switches il and II to the terminals 1 and l ofthe motor 1, and the terminal '1 of the motor I is connected to the lineL Therefore, when the relay contact arm I 2 is deflected in onedirection or the other the terminal l or 1 is energized, causing themotor I to rotate in one direction or the other, thereby varying thevalue of the resistors 3, 3 and 3 and thus the speed of the motor I, andat the same time varying the potential which is impressed upon the barin by the cooperation of brush 9 with receiver resistor I.

If the potential difference between the brush ll and the bar ID is zero,no current flows through the windings i2, and the relay is in its centerposition so that the motor 1 stands still and the motor I runs at aspeed depending upon the position of the commutator 4, which in turncorresponds to the position of the contact ii. If, on the other hand, apotential difference exists between the contact H and the bar In, thecontact arm ll of relay i2 is deflected in one direction or the otherand the motor 1 is energized to shift the nut 5 in the proper direction,to change the values of resistors I and 8 until a balance is againrestored.

The limit switches l3 and l3 are arranged adjacent to the low speedposition and the high speed position, respectively, of the traveling nut5. They are normally closed and are opened by an abutment 5 attached toand movable with the traveling nut 5, when the nut reaches an extremeposition, corresponding to maximum or zero resistance, respectively, inthe secondary circuit 3 of the motor.

The system is further provided with a normally closed stop button H,normally open running button I5, normally open inching button 16, andthe aforementioned electromagnetic relay ll, having an energizingwinding il normally open contacts i'l l'l 11 and I! and normally closedcontacts ll.

The aforementioned double-throw safety switch i 8 may be installed onthe print: no press. The switch is provided with stationary contacts l8and i8 and with a movable contact l8 which may be selectively connectedto one or the other of the stationary contacts. The switch i8 is of wellknown form and is so arranged that it normally completes a circuitthrough the movable contact 18 and stationary contact 18' and isarranged to open this circuit and at the same time to close a circuitthrough contact i8 if the paper in the printing machine should notproperly register, or, if desired, the safety switch :8 may serve otherpurposes.

As afor mentioned, the contact i8 is connected in series with thenormally open contac s 51 while the movable contact i8 is connected inseries with the coils ll of relay it. One of the selectable slow speedtaps i i is also normally connected to the contact iB through "henormally closed contacts il while 'ti ii for the creeping speed isconnected to the contact i8 Hence, when the contact ii! is moved by thepress from its normal position it opens the circuit to contact l8 andcloses a circuit to contact l8 to connect the creeping resistancedirectly to the coils I2 01. the relay l2.

Connected between the terminal 1 and line L and between terminal 1' andline 12, respectively, are the primary windings I! and 20' oftransformers l9 and 20, respectively. The secondary winding I9 of thetransformer I9 is connected in series with a magnetizing coil I2,mounted in cooperative relationship with one of the magnetic cores i2 ofthe relay l2, while a secondary winding 20 is connected in a similarrelationship to the other coll I2 of the relay I2. The connections ofthese windings are such that when the contact arm l2 makes contact withthe stationary contact l2 or IZ respectively, one or the other of thesecondary winding l or 20' is connected in series with the respectivecoil i2 or 12, across the lines L and L to amplify the effect ofenergization oi the coils l2 upon the cores I2 to effect movement ofcontact aim I2. As a current is induced in the winding l9 or 20 by thecurrent flowing in the respective primary winding i9 or 20, the pull onthe respective magnet core I2 is increased.

The connections of the control circuits are as follows: A circuit leadsfrom line L through the stop pushbutton ll, thence through the runpushbutton l5, when depressed, through the energizing coil H, to line L.Another circuit extends from line L through the stop pushbutton H, thenormally open contacts ll (when closed) through the magnetizing winding2 to line L and a further circuit extends from the contacts ll throughthe contacts ll contacts 2*, contacts I1, coil ll to line L. Stillanother circuit extends from line L through the stop pushbutton I4, theinch pushbutton l6 (when closed) thence through coil 2 to line L, andalso through contacts il 2 and il through coil ll to line L.

The system operates as follows: If, with the lines L, L and L energized,it is desired to start the motor and run it at a given high speed, thecontact li is adjusted or set to a point on the sending rheostat llcorresponding to such speed. Thereafter the run button I5 is momentarilydepressed. This energizes the relay coil l1 and the relay ll closes,thereby closing the contacts H which energizes the main switch 2.

Closure of the main switch 2 connects the primary or stator winding oi!the motor I to the lines L, L and L and current flows through thesecondary or rotor winding. Energization of relay ll also closes thecontacts ll ll and I! and opens contacts I1 Energization of switch 2closes contacts 2. A holding circuit is thereby established for the coilH from line L over stop button l4, and contacts li 11 2, 11 through saidcoil I 1, so that the run button l5 may be released, and the relay i7and the main switch 2 remain energized. If a potential difference existsbetween the bus bar i0 and the contact li a current flows in one or theother direction between H through contacts l1, switch ll, through coilsl2, and bus bar Hi' This causes deflection of the contact arm l2 ofrelay I! to energize the motor 1 in one direction or the other, therebycausing movement of the commutater 4 in the desired direction, until thepositions of the traveling nut 5 and of the commutators 9 4 correspondto the position of the contact i l whereupon the arm I 2 of relay l2returns to center position and deenergizes the motor 1.

' means and arranged The motor I then continues to operate at thedesired speed.

When the terminals l or 1 are connected to the line L through the relay!2, the primary winding 2i) .or 19 of one or the other of thetransformers 20 or I9 is also energized. This causes a current to flowin the winding 20* or l9", which current energizes the correspondingcoil l2 r l2 of relay 12, thereby amplifying the torque of the-latteruntil such time as the current in the coils I2 becomes zero. Only one ofthe magnet cores I2 will then be magnetized by the current in the coill2 or I2 as the case may be, and the resulting pull is only a smallfraction of the pull created by the coils I! when energized. As aresult, the relay l2, responding to the centerbiasing means thereof,returns to the oflf position to deenergize the motor I as aforedescribedand at the same time the transformer 19 or 20 is deenergized.

Upon pressing of the stop button I, the main switch 2 and the relay I1are deenergized and the motor I is disconnected from the line. At thesame time the contacts l'l are opened and the contacts l1 are closed.The contacts I1 establish a circuit from a selected slow speed tap llthrough the contact H, the relay coils l2 to the bus bar 10, whichcauses the motor I to be energized to return the traveling nut 5 to aposition corresponding to the voltage at the tap li so that uponreconnection of the motor by the operation of the run button I5 or theinch button IS the secondary resistance in the motor circuit is of suchvalue as to operate the motor I at the desired torque. I If it isdesired to inch the equipment the button i6 is depressed. This energizesthe main switch 2 but the relay ll remains deenergized so that the relaycoils I: are controlled by one of the adjustable tap connections I I andthe motor will only operate at the low speed corresponding to arelatively high torque.

If the safety switch I8 is operated at any time to efiect disengagementof its movable contact Hi from stationary contact I8 and engagement ofthe former with stationary contact l8", it dis- -connects the windingsl2 from either the contact H or the tap li and connects them to the tapH As a result of this connection the current flow in the relay windingcauses the energization of the motor I and return of the crosshead 4 tothe position of maximum resistance in the circuit of the motor I so thatthe printing press is operated at a, creeping speed until adjustment ofthe press is made and the safety switch is again thrown into the normaloperating position.

We claim:

1. In a system operable at different speeds, in combination, an electricmotor, a variable resistor for regulating the speed of said motor,electromagnetic reversing means adapted to vary said resistor, apotentiometer receiver supplied with a constant input voltage andaflording a variable output voltage, means connected to said reversin tovary the output voltage of said receiver in accordance with thevariations of said regulating resistor, a potentiometer sender suppliedwith a constant input voltage and provided with means affording a firstoutput voltage corresponding to a desired running speed, and a secondoutput voltagecorresponding to a creeping speed of said motor, meansadapted to control said reversing means in response'to the differencebetween the output voltage or said receiver and one of the outputvoltages of said sender, mean: to subject said last mentioned means tothe out-' put voltage of said receiver and of the first sender outputvoltage, and associated means operable under certain conditions toautomatically terminate the influence of said first sender outputvoltage upon said voltage difference responsive means and to subjectsaid means to the influence of said second sender output voltage.

2. In a system operable at different speeds, in combination, an electricmotor, a variable resistor for regulating the speed of said motor,electromagnetic reversing means adapted to vary said resistor, apotentiometer receiver supplied with a constant input voltage andaffording a variable output voltage, means connected to said reversingmeans for varying the output voltage of said receiver in accordance withthe variations of said regulating resistor, a potentiometer sendersupplied with a constant input voltage and provided with means affordinga first output voltage corresponding to a desired running speed, asecond output voltage corresponding to a desired value of said resistorfor starting and inching said motor, and a third output voltage.corresponding to a creeping speed of said motor, means adapted tocontrol said electromagnetic means in response to the difference betweenthe output voltage of said receiver and one or another of the outputvoltages of said sender, means for inching and running said motorincluding an electromagnetic switch to connect it to a source of currentsupply and to subject said voltage difference responsive means to theoutput voltage of said receiver and of the first or second sender outputvoltage, selectively, and means operable in response to abnormalconditions of the system to eliminate the influence of said first orsaid second sender output voltage upon said voltage differenceresponsive means and to subject the latter to the influence of saidthird sender output voltage.

3. In a drive for printing presses and. the like, in combination, avariable speed driving motor, a speed regulating resistor in circuitwith said motor, a reversible pilot motor for varying said resistor, areceiver comprising a potentiometer supplied with a constant inputvoltage and affording a variable output voltage, means operable by saidpilot motor for varying the output voltage of said receiver inaccordance with variations of said resistor, a sender comprising apotentiometer supplied with a constant input voltage and provided withmeans afiording, a first output voltage corresponding to a desiredrunning speed of said driving motor, a second output voltagecorresponding to a desired value of said regulating resistor forstarting and inching said driving motor, and a third output voltagecorresponding to a creeping speed of said driving motor, a reversingrelay adapted to control said pilot motor in response to the differencebetweenthe receiver output voltage and one of the sender ouput voltages,an inching pushbutton switch and a running pushbutton switch, bothbiased to open position, an electromagnetic switch energizable by saidinching switch to connect said motor to a source of current supply, anelectromagnetic relay energizable by closure of said running switch,said electromagnetic relay being adapted when deenergized to subjectsaid reversing relay to said second sender ouput voltage and whenenergized to energize said electromagnetic switch and to subject saidreversing relay to said first sender output voltage and to complete amaintaining circuit paralleling said running switch, and a switchresponsive to a condition of said printing press and adapted uponresponse to terminate the influence of said first or second senderoutput voltage upon said reversing relay and to subject it to said thirdsender output voltage, and a normally closed pushbutton switch operableto deenergize said electromagnetic relay and said electromagneticswitch.

4. In a drive for printing presses and the like, in combination, avariable speed driving motor, a speed regulating resistor in circuitwith said motor, a reversible pilot motor for varying said resistor, areceiver comprising a potentiometer supplied with a constant inputvoltage and affording a variable output voltage, means operable by saidpilot motor for varying the output voltage of said receiver inaccordance with variations of said resistor, a sender comprising apotentiometer supplied with a constant input volt age and provided withmeans of affording, a first output voltage corresponding to a desiredrunning speed of said driving motor, a second output voltagecorresponding to a desired value of said regulating resistor forstarting and inching said driving motor, and a third output voltagecorresponding to a creeping speed of said driving motor, a reversingrelay adapted to control said pilot motor in response to the differencebetween the receiver output voltage and one of the sender outputvoltages, an inching pushbutton switch and a running pushbutton switch,both biased to open position, an electromagnetic switch energizable bysaid inching switch to connect said motor to a source of current supply,an electromagnetic relay energizable by the closure of said runningswitch, said electromagnetic relay being adapted when deenergized tosubject said reversing relay to said second sender output voltage andadapted when energized to energize said electromagnetic switch, and tosubg ect said reversing relay to said first output voltage and to closea maintaining c'rcuit paralleling said running switch, and a normallyclosed pushbutton switch operable to deenergize said electromagneticrelay and said electromagnetic switch.

5. In a drive for printing presses and the like, in combination, avariable speed driving motor, a speed regulating resistor in circuitwith said motor, a reversible pilot motor for varying said resistor, areceiver comprising a potentiometer supplied with a constant inputvoltage and affording a variable output voltage, means operable by saidpilot motor for varying the output voltage of said receiver inaccordance with variations of said resistor, a sender comprising apotentiometer supplied with a constant input voltage and provided withmeans of aifording, a first output voltage corresponding to a desiredrunning speed of said driving motor, a second output voltagecorresponding to a desired value of said regulating resistor forstarting and inching said drivin motor, a third output voltagecorresponding to a creeping speed of said driving motor, a reversingrelay adapted to control said pilot motor in response to the difi'erencebetween the receiver output voltage and one of the sender outputvoltages, an inching pushbutton switch and a running pushbutton switch,both biased to open position, an electromagnetic switch energizable bysaid inching pushbutton switch to connect said motor to a source ofcurrent supply, an electromagnetic relay normally subjecting saidreversing relay to said second output voltage and energizable byoperation of said running pushbutton switch to terminate the effect ofsaid second output voltage upon said reversing relay and subjecting itto said first output voltage and to complete an energizing circuit forsaid electromagnetic switch, and a normally closed stop switch operableto deenergize said electromagnetic relay and said electromagneticswitch.

6. In a drive for printing presses and the like, in combination, avariable speed driving motor, a speed regulating resistor in circuitwith said motor, a reversible pilot motor for varying said resistor, areceiver comprising a potentiometer supplied with a constant inputvoltage and affording a variable output voltage, means operable by saidpilot motor for varying the output voltage of said receiver inaccordance with variations of said resistor, a sender comprising apotentiometer supplied with a constant input voltage and provided withmeans affording, a first output voltage corresponding to a desiredrunning speed of said driving motor, a second output voltagecorresponding to a desired value of said regulating resistor forstarting and inching said driving motor, and a third output voltagecorresponding to a creeping speed of said driving motor, a reversingrelay adapted to control said pilot motor in response to the difi'erencebetween the receiver output voltage and one of the sender outputvoltages, an inching pushbutton switch and a running pushbutton switch,both biased to open position, an electromagnetic switch energizable bysaid inching pushbutton switch to connect said motor to a source ofcurrent supply, an electromagnetic relay normally subjecting saidreversing relay to said second output voltage and energizable byoperation of said running switch to terminate the efi'ect of said secondoutput voltage upon said reversing relay and subjecting it to said firstoutput voltage and to complete an energizing circuit for saidelectromagnetic switch, a normally closed stop switch operable todeenergize said electromagnetc relay and said electromagnetic switch,and a switch responsive to an operating condition of said printing pressand adapted upon response to terminate the influence of said first orsecond sender output voltage upon said reversing relay and to subject itto said third sender output voltage.

EDWIN W. SEEGER.

CARROLL STANSBURY.

